Antireflective coatings for metasurfaces

Abstract

To provide an anti-reflective coating for a suitable metasurface. Antireflective coatings for metasurfaces are described herein. In some embodiments, the metasurface may include a substrate, a plurality of nanostructures thereon, and an antireflective coating disposed over the nanostructures. The antireflective coating may be a transparent polymer, e.g., a photoresist layer, and may have a refractive index lower than that of the nanostructures and higher than that of the overlying medium (e.g., air). Advantageously, the antireflective coating may reduce or eliminate residual images in augmented reality displays incorporating the metasurface.

Description

[Technical Field]

[0001] This application claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 62 / 451,587, filed January 27, 2017, the entire disclosure of which is incorporated herein by reference.

[0002] This application incorporates by reference the entirety of each of the following patent applications: U.S. Application No. 14 / 555,585, filed November 27, 2014; U.S. Application No. 14 / 690,401, filed April 18, 2015; U.S. Application No. 14 / 212,961, filed March 14, 2014; U.S. Application No. 14 / 331,218, filed July 14, 2014; U.S. Patent Application No. 15 / 342,033, filed November 2, 2016 (Attorney Docket No. MLEAP.027A); U.S. Provisional Application No. 62 / 333,067, filed May 6, 2016 (Attorney Docket No. MLEAP.066PR); and U.S. Provisional Application No. 62 / 451,608, entitled "DIFFRACTION GRATINGS FORMED BY No. 62 / 451,615, entitled "DIFFRACTION GRATINGS BASED ON METASURFACES HAVING ASYMMETRIC OPTICAL- ELEMENTS," filed January 27, 2017 (Attorney Docket No. MLEAP.092PR); and U.S. Provisional Application No. 62 / 451,615, entitled "DIFFRACTION GRATINGS BASED ON METASURFACES HAVING ASYMMETRIC OPTICAL- ELEMENTS," filed January 27, 2017 (Attorney Docket No. MLEAP.103PR).

[0003] The present disclosure relates to optical systems such as display systems, including augmented reality systems. [Background technology]

[0004] Modern computing and display technology has facilitated the development of systems for so-called "virtual reality" or "augmented reality" experiences, in which digitally reproduced images or portions thereof are presented to a user in a manner that appears or can be perceived as real. Virtual reality or "VR" scenarios typically involve the presentation of digital or virtual image information without transparency to other actual real-world visual input, while augmented reality or "AR" scenarios typically involve the presentation of digital or virtual image information as an augmentation to the user's visualization of the real world around them. Mixed reality or "MR" scenarios are a type of AR scenario that typically involve virtual objects integrated into and responsive to the natural world. For example, MR scenarios may include AR image content that appears blocked by or is perceived to otherwise interact with objects in the real world.

[0005] Referring to FIG. 1 , an augmented reality scene 10 is depicted. A user of the AR technology sees a real-world park-like setting 20 featuring people, trees, a building in the background, and a concrete platform 30. The user also perceives that they are "seeing" "virtual content," such as a robotic figure 40 standing on the real-world platform 30 and a flying, cartoonish avatar character 50 that appears to be an anthropomorphic bumblebee. These elements 50, 40 are "virtual" in that they do not exist in the real world. The human visual perception system is complex, making it difficult to create AR technology that facilitates a comfortable, natural-feeling, and rich presentation of virtual image elements among other virtual or real-world image elements.

[0006] The systems and methods disclosed herein address various challenges associated with AR or VR technology. Summary of the Invention [Means for solving the problem]

[0007] According to some embodiments, an optical system is presented herein. In some embodiments, the optical system may include an optically transmissive substrate, a metasurface overlying the substrate, the metasurface comprising a plurality of nanostructures, and an antireflective coating conformally disposed over the nanostructures of the metasurface, the antireflective coating comprising an optically transparent material, the optically transparent material having a refractive index less than that of the nanostructures.

[0008] According to some embodiments, the antireflective coating is an interference coating. In some embodiments, the metasurface comprises a diffraction grating. In some embodiments, the metasurface comprises an asymmetric diffraction grating. In some embodiments, the metasurface comprises a Pancharatnam Berry Phase Optical Element (PBOE). In some embodiments, the metasurface comprises a multi-stage nanostructure. In some embodiments, the optically transparent material comprises a polymer. In some embodiments, the optically transparent material comprises a photoresist. In some embodiments, the optically transparent material has a refractive index between about 1.2 and about 2. In some embodiments, the distance from the top surface of the nanostructures to the top surface of the antireflective coating is between about 10 nm and about 1 micron. In some embodiments, the distance from the top surface of the nanostructures to the top surface of the antireflective coating is between about 30 nm and about 250 nm. In some embodiments, the antireflective coating forms a planarizing layer extending between and across the nanostructures.

[0009] According to some other embodiments, presented herein is an optical system comprising an antireflective coating for an optical element comprising a metasurface, the antireflective coating comprising a layer of optically transparent material having a refractive index greater than 1 and less than the refractive index of the material comprising the metasurface, the layer of polymeric material being conformally disposed over the metasurface.

[0010] According to some embodiments, the optically transparent material comprises a polymer. In some embodiments, the optically transparent material comprises a photoresist. In some embodiments, the optically transparent material has a refractive index between about 1.2 and about 2. In some embodiments, the distance from the top surface of the metasurface to the top surface of the antireflective coating is between about 10 nm and about 1 micron. In some embodiments, the antireflective coating reduces the amount of incident light reflected by the metasurface by more than about 50% compared to the amount of incident light reflected by a substantially similar metasurface without the antireflective coating. In some embodiments, the incident light has an angle of incidence between about -50° and 50°.

[0011] According to yet other embodiments, a method for forming an antireflective coating on a metasurface is provided. In some embodiments, the method may include providing an optically transmissive substrate comprising a metasurface, the metasurface comprising a plurality of nanostructures, and depositing a layer of optically transparent material over the plurality of nanostructures, the layer of optically transparent material forming the antireflective coating.

[0012] In some embodiments, the optically transparent material comprises a polymer. In some embodiments, the optically transparent material comprises a photoresist. In some embodiments, a distance from a top surface of the nanostructures to a top surface of the formed antireflective coating is between about 10 nm and about 1 micron. In some embodiments, conformally depositing the optically transparent material comprises spin-coating the optically transparent material over the nanostructures. In some embodiments, conformally depositing the optically transparent material comprises performing a chemical vapor deposition (CVD) process.

[0013] Various additional embodiments are provided below.

[0014] 1. An optical system comprising: an optically transparent substrate; a metasurface overlying a substrate, the metasurface comprising a plurality of nanostructures; an antireflective coating comprising an optically transparent material conformally disposed over the nanostructures of the metasurface, the optically transparent material having a refractive index less than the refractive index of the nanostructures; An optical system comprising:

[0015] 2. The optical system of embodiment 1, wherein the anti-reflective coating is an interference coating.

[0016] 3. The optical system of embodiment 1, wherein the metasurface comprises a diffraction grating.

[0017] 4. The optical system of embodiment 3, wherein the metasurface comprises an asymmetric diffraction grating.

[0018] 5. The optical system of any one of embodiments 1-3, wherein the metasurface comprises a Pancharatnam Berry phase optical element (PBOE).

[0019] 6. The optical system of embodiment 1, wherein the metasurface comprises a multi-stage nanostructure.

[0020] 7. The optical system of any one of embodiments 1-6, wherein the optically transparent material comprises a polymer.

[0021] 8. The optical system of embodiment 7, wherein the optically transparent material comprises a photoresist.

[0022] 9. The optical system of any one of embodiments 1-8, wherein the optically transparent material has a refractive index of about 1.2 to about 2.

[0023] 10. The optical system of any one of embodiments 1-9, wherein the distance from the top surface of the nanostructure to the top surface of the anti-reflective coating is from about 10 nm to about 1 micron.

[0024] 11. The optical system of embodiment 10, wherein the distance from the top surface of the nanostructure to the top surface of the antireflective coating is between about 30 nm and about 250 nm.

[0025] 12. The optical system of any one of embodiments 1-11, wherein the anti-reflective coating forms a planarizing layer that extends between and over the nanostructures.

[0026] 13. An optical system comprising: 1. An anti-reflective coating for an optical element comprising a metasurface, the anti-reflective coating comprising: a layer of optically transparent material having a refractive index greater than 1 and less than the refractive index of the material comprising the metasurface; a layer of polymer material conformally disposed over the metasurface; Anti-reflective coating An optical system comprising:

[0027] 14. The antireflective coating of embodiment 13, wherein the optically transparent material comprises a polymer.

[0028] 15. The antireflective coating of embodiment 14, wherein the optically transparent material comprises a photoresist.

[0029] 16. The antireflective coating of any one of embodiments 13-15, wherein the optically transparent material has a refractive index of about 1.2 to about 2.

[0030] 17. The antireflective coating of any one of embodiments 13-16, wherein the distance from the top surface of the metasurface to the top surface of the antireflective coating is from about 10 nm to about 1 micron.

[0031] 18. An antireflective coating according to any one of embodiments 13-17, wherein the antireflective coating reduces the amount of incident light reflected by the metasurface by more than about 50% compared to the amount of incident light reflected by a substantially similar metasurface without the antireflective coating.

[0032] 19. The antireflective coating of embodiment 18, wherein the incident light has an angle of incidence of about -20° to 20°.

[0033] 20. A method for forming an antireflective coating on a metasurface, the method comprising: providing an optically transparent substrate comprising a metasurface, the metasurface comprising a plurality of nanostructures; depositing a layer of optically transparent material over the plurality of nanostructures; Including, The layer of optically transparent material forms an anti-reflective coating.

[0034] 21. The method of embodiment 20, wherein the optically transparent material comprises a polymer.

[0035] 22. The method of embodiment 21, wherein the optically transparent material comprises a photoresist.

[0036] 23. The method of any one of embodiments 20-22, wherein the distance from the top surface of the nanostructure to the top surface of the antireflective coating formed is from about 10 nm to about 1 micron.

[0037] 24. The method of any one of embodiments 20-23, wherein conformally depositing the optically transparent material comprises spin-coating the optically transparent material over the nanostructures.

[0038] 25. The method of any one of embodiments 20-23, wherein conformally depositing the optically transparent material comprises performing a chemical vapor deposition (CVD) process. The present invention provides, for example, the following. (Item 1) 1. An optical system comprising: an optically transparent substrate; a metasurface overlying the substrate, the metasurface comprising a plurality of nanostructures; an antireflective coating comprising an optically transparent material conformally disposed over the nanostructures of the metasurface, the optically transparent material having a refractive index less than that of the nanostructures; An optical system comprising: (Item 2) Item 10. The optical system of item 0, wherein the anti-reflection coating is an interference coating. (Item 3) Item 10. The optical system of item 0, wherein the metasurface comprises a diffraction grating. (Item 4) Item 10. The optical system of item 0, wherein the metasurface comprises an asymmetric diffraction grating. (Item 5) Item 10. The optical system of item 0, wherein the metasurface comprises a Pancharatnam Berry phase optical element (PBOE). (Item 6) Item 0. The optical system of item 0, wherein the metasurface comprises a multi-stage nanostructure. (Item 7) Item 10. The optical system of item 0, wherein the optically transparent material comprises a polymer. (Item 8) Item 10. The optical system of item 0, wherein the optically transparent material comprises a photoresist. (Item 9) Item 10. The optical system according to item 0, wherein the optically transparent material has a refractive index of about 1.2 to about 2. (Item 10) Item 10. The optical system of item 0, wherein the distance from the top surface of the nanostructure to the top surface of the anti-reflective coating is about 10 nm to about 1 micron. (Item 11) Item 10. The optical system of item 0, wherein the distance from the top surface of the nanostructure to the top surface of the anti-reflective coating is about 30 nm to about 250 nm. (Item 12) Item 0-0. The optical system of any one of items 0-0, wherein the anti-reflective coating forms a planarizing layer extending between and across the nanostructures. (Item 13) 1. An optical system comprising: 1. An anti-reflective coating for an optical element comprising a metasurface, the anti-reflective coating comprising: a layer of optically transparent material having a refractive index greater than 1 and less than the refractive index of a material comprising the metasurface; a layer of polymeric material conformally disposed over the metasurface; Anti-reflective coating An optical system comprising: (Item 14) 10. The anti-reflective coating of claim 0, wherein the optically transparent material comprises a polymer. (Item 15) Item 10. The antireflective coating of item 0, wherein the optically transparent material comprises a photoresist. (Item 16) 10. The anti-reflective coating of claim 0, wherein the optically transparent material has a refractive index of about 1.2 to about 2. (Item 17) 10. The antireflective coating according to claim 0, wherein the distance from the top surface of the metasurface to the top surface of the antireflective coating is from about 10 nm to about 1 micron. (Item 18) 10. The antireflective coating of claim 0, wherein the antireflective coating reduces the amount of incident light reflected by the metasurface by more than about 50% compared to the amount of incident light reflected by a substantially similar metasurface that does not include the antireflective coating. (Item 19) Item 19. The anti-reflective coating according to item 18, wherein the incident light has an incident angle of about -20° to 20°. (Item 20) 1. A method for forming an anti-reflective coating on a metasurface, the method comprising: providing an optically transparent substrate comprising a metasurface, the metasurface comprising a plurality of nanostructures; depositing a layer of optically transparent material over the plurality of nanostructures; Including, The layer of optically transparent material forms the anti-reflective coating. (Item 21) Item 10. The method of item 0, wherein the optically transparent material comprises a polymer. (Item 22) Item 10. The method of item 0, wherein the optically transparent material comprises a photoresist. (Item 23) Item 0. The method of any one of items 0-0, wherein the distance from the top surface of the nanostructure to the top surface of the formed antireflective coating is from about 10 nm to about 1 micron. (Item 24) Item 10. The method of item 0, wherein conformally depositing the optically transparent material comprises spin-coating the optically transparent material over the nanostructures. (Item 25) Item 10. The method of item 0, wherein conformally depositing the optically transparent material comprises performing a chemical vapor deposition (CVD) process. [Brief explanation of the drawings]

[0039] [Figure 1] FIG. 1 illustrates a user's view of an augmented reality (AR) device.

[0040] [Figure 2] FIG. 2 illustrates an example of a wearable display system.

[0041] [Figure 3] FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user.

[0042] [Figure 4] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes.

[0043] [Figure 5]5A-5C illustrate the relationship between the radius of curvature and the radius of focus.

[0044] [Figure 6] FIG. 6 illustrates an embodiment of a waveguide stack for outputting image information to a user.

[0045] [Figure 7] FIG. 7 illustrates an example of an output beam output by a waveguide.

[0046] [Figure 8] FIG. 8 illustrates an example of a stacked waveguide assembly where each depth plane contains an image formed using multiple different primary colors.

[0047] [Figure 9A] FIG. 9A illustrates a cross-sectional side view of an example of a set of stacked waveguides, each containing an internal coupling optical element.

[0048] [Figure 9B] FIG. 9B illustrates a perspective view of the multiple stacked waveguide embodiment of FIG. 9A.

[0049] [Figure 9C] FIG. 9C illustrates a top-down plan view of the multiple stacked waveguide embodiment of FIGS. 9A and 9B.

[0050] [Figure 10] FIG. 10 illustrates a cross-sectional side view of an exemplary optical structure including a metasurface and an anti-reflective coating.

[0051] [Figure 11A] FIG. 11A illustrates a top-down view of an exemplary metasurface comprising an asymmetric Pancharatnam Berry phase optical element (PBOE).

[0052] [Figure 11B]FIG. 11B illustrates a perspective view of the metasurface of FIG. 11A with a top anti-reflective coating.

[0053] [Figure 11C] FIG. 11C is a plot of transmission and reflection as a function of the angle of incidence of light for an optical structure having the general structure shown in FIGS. 11A-11B.

[0054] [Figure 12A] FIG. 12A illustrates a cross-sectional perspective view of an exemplary metasurface comprising an asymmetric diffraction grating and an anti-reflection coating.

[0055] [Figure 12B] FIG. 12B illustrates a cross-sectional side view of the exemplary metasurface and antireflective coating of FIG.

[0056] [Figure 12C] FIG. 12C is a plot of the transmission and reflection spectra for the optical structure of FIGS. 12A-12B.

[0057] [Figure 13] 13A-13D are cross-sectional views of intermediate structures at various stages in the fabrication of an exemplary optical structure comprising a metasurface, according to some embodiments.

[0058] [Figure 14] 14A-14D are cross-sectional views of intermediate structures at various stages in the fabrication of an exemplary optical structure comprising a metasurface, according to some embodiments.

[0059] [Figure 15] FIG. 15 illustrates a cross-sectional side view of a metasurface with a conformal anti-reflective coating. DETAILED DESCRIPTION OF THE INVENTION

[0060] Metasurfaces, also referred to as metamaterial surfaces, offer the opportunity to achieve virtually flat, aberration-free optics at scales much smaller than geometric optics. Without being limited by theory, in some embodiments, metasurfaces comprise dense arrays of surface structures or nanostructures that function as resonant optical antennas. The resonant nature of the interaction between light and the surface structures provides the ability to manipulate optical wavefronts. In some cases, metasurfaces may enable the replacement of bulky or difficult-to-manufacture optical components with thin, planar elements formed by simple patterning processes.

[0061] It should be understood that optical elements formed from metasurfaces can function in reflective and / or transmissive modes. In reflective mode, the metasurface may reflect light at a desired angle. In transmissive mode, the metasurface may transmit light through the body of the metasurface while also deflecting the light at a desired angle. Undesirably, metasurfaces operating in transmissive mode may also reflect incident light, for example, due to Fresnel reflections at interfaces with other materials. Additionally, for metasurfaces operating in reflective mode, the angle at which the metasurface is configured to reflect light may differ from the angle at which light is reflected from the interface.

[0062] Unfortunately, unintended reflections by a metasurface can cause optical artifacts. For example, in a display device in which a metasurface is used as an optical element to direct light encoded with image content (e.g., light modified by a spatial light modulator), reflections can cause a residual image due to the round-trip reflection of some of the light along the optical path before reaching the user. For example, the metasurface may form an internal coupling optical element configured to internally couple light into a waveguide and thus output image content to the user. If some of this light is reflected rather than internally coupled into the waveguide, the reflected light may backpropagate to the light projector or light source, which may then reflect the light back to the metasurface for internal coupling into the waveguide and ultimately output to the user. Due to this round-trip reflection, light from a previous video image frame may be provided to the waveguide along with the light encoding the current image frame. The light encoding the previous image frame may be visible to the user as a residual image, which reduces the image quality of the display device.

[0063] In some embodiments, an antireflective coating can reduce or eliminate reflection of light from the metasurface. The antireflective coating can be formed from an optically transparent layer of material, such as a polymer layer, e.g., a layer of photoresist. In some embodiments, no air or other material can be present between the metasurface and the antireflective coating. That is, the antireflective coating can be in direct contact with the metasurface. The material forming the antireflective coating can have a refractive index lower than that of the nanostructures of the metasurface, but higher than that of the material or medium (e.g., air) that forms the interface between the metasurface and the opposing antireflective coating.

[0064] In some embodiments, the antireflective coating may be an interference coating, where the thickness of the layer of material is selected to provide destructive interference between light reflecting from the top and bottom surfaces of the layer. Preferably, the thickness of the layer is selected to provide this interference for light in visible wavelengths. In some embodiments, the metasurface may be part of a color display utilizing multiple primary colors. As a result, a particular metasurface may be exposed only to light of an associated limited range of wavelengths corresponding to a particular primary color, and the antireflective coating may have a thickness selected to provide interference for light having this associated limited range of wavelengths.

[0065] In some embodiments, the antireflective coating may be a planar layer that extends across and between the nanostructures that form the metasurface, forming a planar surface of the nanostructures. Such a planar layer may advantageously provide antireflective properties over a wide range of incident angles of light. In some embodiments, the antireflective coating may be a conformal layer that is disposed on the surface of the nanostructures that form the metasurface. The conformal layer may be continuous, extending across and between multiple nanostructures, or may be isolated on individual ones of the nanostructures.

[0066] Advantageously, the reduction in reflection can reduce or eliminate optical effects such as persistence of light, thereby enabling a display device to output images with higher perceived quality. In some embodiments, the antireflective coating can reduce the amount of light reflected by the metasurface by about 50%, 75%, 85%, 90%, 95%, 99%, or more compared to the same structure without the antireflective coating. Antireflective coatings can be particularly advantageously applied to metasurfaces operating in a transmissive mode, where reflection is not part of the metasurface's design.

[0067] Reference is now made to the drawings, wherein like reference numerals refer to like parts throughout.

[0068] In some embodiments, metasurfaces may be advantageously applied to form optical elements within display devices, such as those for AR or VR display systems. These display systems may display virtual content to a user or viewer, and AR systems may also allow users to see the world around them by transmitting light from the surrounding environment to the user's eyes. Preferably, this virtual content is displayed on a wearable head-mounted display, for example, as part of eyewear that projects image information to the user's eyes. As used herein, it should be understood that a "head-mounted" display is a display that may be mounted on the viewer's head.

[0069] FIG. 2 illustrates an example of a wearable display system 80. The display system 80 includes a head-mounted display 62 and various mechanical and electronic modules and systems to support the functionality of the display 62. The display 62 may be coupled to a frame 64, which is wearable by a display system user or viewer 60 and configured to position the display 62 directly in front of the user's 60 eyes. The display 62, in some embodiments, may be considered eyewear. In some embodiments, a speaker 66 is coupled to the frame 64 and positioned adjacent to the user's 60 ear canal (in some embodiments, another speaker, not shown, is positioned adjacent the user's other ear canal to provide stereo / adjustable sound control). In some embodiments, the display system may also include one or more microphones 67 or other devices to detect sound. In some embodiments, the microphones are configured to allow a user to provide input or commands (e.g., voice menu command selections, natural language queries, etc.) to the system 80 and / or enable audio communication with other persons (e.g., other users of similar display systems). The microphone may further be configured as an ambient sensor to continuously collect audio data (e.g., to passively collect from the user and / or the environment). Such audio data may include user sounds, such as heavy breathing, or environmental sounds, such as a commotion, indicative of a nearby event. The display system may also include an ambient sensor 30a, which may be separate from the frame 64 and attached to the body of the user 60 (e.g., on the head, torso, limbs, etc. of the user 60). The ambient sensor 30a, in some embodiments, may be configured to obtain data characterizing a physiological state of the user 60, as described further herein. For example, the sensor 30a may be an electrode.

[0070] FIG. 2 illustrates an example of a wearable display system 60. The display system 60 includes a display 70 and various mechanical and electronic modules and systems to support the functionality of the display 70. The display 70 may be coupled to a frame 80, which is wearable by a display system user or viewer 90 and configured to position the display 70 directly in front of the user's 90 eyes. The display 70 may be considered eyewear in some embodiments. In some embodiments, a speaker 100 is coupled to the frame 80 and configured to be positioned adjacent to the user's 90 ear canal (in some embodiments, another speaker, not shown, may optionally be positioned adjacent the user's other ear canal to provide stereo / shapeable sound control). The display system may also include one or more microphones 110 or other devices to detect sound. In some embodiments, the microphone may be configured to allow a user to provide input or commands to system 60 (e.g., selecting voice menu commands, natural language questions, etc.) and / or enable audio communication with other persons (e.g., other users of similar display systems). The microphone may also be configured as an ambient sensor to collect audio data (e.g., sounds from the user and / or the environment). In some embodiments, the display system may also include ambient sensor 120a, which may be separate from frame 80 and attached to the body of user 90 (e.g., on the head, torso, limbs, etc. of user 90). Ambient sensor 120a, in some embodiments, may be configured to acquire data characterizing a physiological state of user 90. For example, sensor 120a may be an electrode.

[0071] 2, the display 70 is operably coupled by a communication link 130, such as wired or wireless connectivity, to a local data processing module 140, which may be mounted in a variety of configurations, such as fixedly attached to the frame 80, fixedly attached to a helmet or hat worn by the user, embedded within headphones, or otherwise removably attached to the user 90 (e.g., in a backpack-style configuration, a belt-type configuration). Similarly, the sensor 120a may be operably coupled to the local data processing module 140 by a communication link 120b, e.g., wired or wireless connectivity. The local processing and data module 140 may comprise a hardware processor and digital memory, such as non-volatile memory (e.g., flash memory or a hard disk drive), both of which may be utilized to aid in processing, caching, and storing data. The data includes a) data captured from sensors (such as image capture devices (cameras, etc.), microphones, inertial measurement units, accelerometers, compasses, GPS units, wireless devices, gyroscopes, and / or other sensors disclosed herein (e.g., which may be operatively coupled to frame 80 or otherwise attached to user 90)) and / or b) data obtained and / or processed using remote processing module 150 and / or remote data repository 160 (including data related to virtual content), possibly for processing or retrieval and then passage to display 70. Local processing and data module 140 may be operatively coupled to remote processing module 150 and remote data repository 160 by communication links 170, 180, such as via wired or wireless communication links, such that these remote modules 150, 160 are operatively coupled to each other and available as resources to local processing and data module 140. In some embodiments, the local processing and data module 140 may include one or more of an image capture device, a microphone, an inertial measurement unit, an accelerometer, a compass, a GPS unit, a wireless device, and / or a gyroscope.In some other embodiments, one or more of these sensors may be mounted on the frame 80 or may be freestanding structures that communicate with the local processing and data module 140 via wired or wireless communication paths.

[0072] 2 , in some embodiments, remote processing module 150 may comprise one or more processors configured to analyze and process data and / or image information. In some embodiments, remote data repository 160 may comprise a digital data storage facility that may be available through the Internet or other networking configuration in a “cloud” resource configuration. In some embodiments, remote data repository 160 may include one or more remote servers that provide information, for example, information for generating augmented reality content, to local processing and data module 140 and / or remote processing module 150. In some embodiments, all data is stored and all computations are performed within the local processing and data module, allowing for fully autonomous use from the remote module.

[0073] Referring now to FIG. 3, the perception of an image as “three-dimensional” or “3-D” can be achieved by providing a slightly different presentation of the image to each eye of a viewer. FIG. 3 illustrates a conventional display system for simulating a three-dimensional image for a user. Two distinct images 190, 200, one for each eye 210, 220, are output to the user. The images 190, 200 are spaced from the eyes 210, 220 by a distance 230 along an optical axis, or z-axis, parallel to the viewer's line of sight. The images 190, 200 are flat, and the eyes 210, 220 can focus on the images by assuming a single accommodative state. Such a 3-D display system relies on the human visual system to combine the images 190, 200 and provide the perception of depth and / or scale of the combined image.

[0074] However, it should be understood that the human visual system is more complex and providing a realistic perception of depth is more difficult. For example, many viewers of conventional “3-D” display systems find such systems uncomfortable or may not perceive any sense of depth at all. Without being limited by theory, it is believed that a viewer of an object may perceive the object as “three-dimensional” due to a combination of vergence and accommodation. The vergence movement of two eyes relative to each other (i.e., the rotation of the eyes, in which the pupils move toward or away from each other to converge the lines of sight of the eyes and fixate on an object) is closely linked to the focusing (or “accommodation”) of the eye's lens and pupil. Under normal conditions, changing the focus of the eye's lens or accommodating the eye and shifting focus from one object to another at a different distance will automatically produce a matching change in convergence to the same distance, a relationship known as the "accommodation-vergence reflex" and pupil dilation or constriction. Similarly, changes in convergence will, under normal conditions, induce a matching change in accommodation in lens shape and pupil size. As described herein, many stereoscopic or "3-D" display systems display a scene using slightly different presentations (and therefore slightly different images) to each eye so that a three-dimensional perspective is perceived by the human visual system. However, such systems, among other things, simply provide different presentations of a scene, but are uncomfortable for many viewers because the eyes view all image information in a single, accommodated state, working against the "accommodation-vergence reflex." Display systems that offer better matching between accommodation and convergence may produce a more realistic and comfortable simulation of three-dimensional images.

[0075] FIG. 4 illustrates aspects of an approach for simulating a three-dimensional image using multiple depth planes. With reference to FIG. 4 , objects at various distances from the eyes 210, 220 on the z-axis are accommodated by the eyes 210, 220 so that the objects are in focus. The eyes 210, 220 assume a particular accommodated state and focus on objects at different distances along the z-axis. As a result, a particular accommodated state may be said to be associated with a particular one of the depth planes 240 having an associated focal length such that an object or portion of an object at a particular depth plane is in focus when the eye is in the accommodated state for that depth plane. In some embodiments, a three-dimensional image may be simulated by providing a different presentation of an image to each eye 210, 220, and by providing a different presentation of an image corresponding to each of the depth planes. While shown as separate for clarity of illustration, it should be understood that the fields of view of the eyes 210, 220 may overlap, for example, as the distance along the z-axis increases. Additionally, although shown as flat for ease of illustration, it should be understood that the contours of the depth plane may be curved in physical space, for example, so that all features within the depth plane are in focus with the eye in a particular accommodated state.

[0076] The distance between an object and the eye 210 or 220 can also change the amount of divergence of light from the object as viewed by that eye. Figures 5A-5C illustrate the relationship between distance and divergence of light rays. The distance between the object and the eye 210 is represented by decreasing distances R1, R2, and R3. As shown in Figures 5A-5C, light rays become more divergent as the distance to the object decreases. As the distance increases, the light rays become more collimated. In other words, the light field generated by a point (an object or part of an object) can be said to have a spherical wavefront curvature that is a function of the distance the point is from the user's eye. The curvature increases as the distance between the object and the eye 210 decreases. As a result, the divergence of light rays at different depth planes also differs, and the divergence increases as the distance between the depth plane and the viewer's eye 210 decreases. While only a single eye 210 is illustrated in FIGS. 5A-5C and various other figures herein for clarity of illustration, it should be understood that the discussion regarding eye 210 may apply to both eyes 210 and 220 of a viewer.

[0077] Without being limited by theory, it is believed that the human eye is typically capable of interpreting a finite number of depth planes to provide depth perception. As a result, a highly realistic simulation of perceived depth can be achieved by providing the eye with different representations of images corresponding to each of these limited number of depth planes. The different representations may be focused separately by the viewer's eyes, thereby serving to provide depth cues to the user based on the ocular accommodation required to focus on different image features for a scene located on the different depth planes and / or based on the observation of different image features on the different depth planes that are out of focus.

[0078] FIG. 6 illustrates an example of a waveguide stack for outputting image information to a user. Display system 250 includes a stack of waveguides or stacked waveguide assembly 260 that can be utilized to provide a three-dimensional perception to the eye / brain using multiple waveguides 270, 280, 290, 300, 310. In some embodiments, display system 250 is system 60 of FIG. 2, and FIG. 6 schematically illustrates some portions of system 60 in greater detail. For example, waveguide assembly 260 may be part of display 70 of FIG. 2. It should be understood that display system 250 may, in some embodiments, be considered a light field display.

[0079] In some embodiments, a single waveguide may be configured to output light with a set amount of wavefront divergence corresponding to a single or limited number of depth planes, and / or the waveguide may be configured to output light of a limited range of wavelengths. As a result, in some embodiments, multiple waveguides or stacks of waveguides may be utilized to provide different amounts of wavefront divergence for different depth planes and / or output light of different ranges of wavelengths. As used herein, it should be understood that a depth plane may follow the contour of a flat or curved surface. In some embodiments, the depth plane may advantageously follow the contour of a flat surface for convenience.

[0080] Continuing with reference to FIG. 6, the waveguide assembly 260 may also include multiple features 320, 330, 340, 350 between the waveguides. In some embodiments, the features 320, 330, 340, 350 may be one or more lenses. The waveguides 270, 280, 290, 300, 310 and / or multiple lenses 320, 330, 340, 350 may be configured to transmit image information to the eye using various levels of wavefront curvature or ray divergence. Each waveguide level may be associated with a particular depth plane and configured to output image information corresponding to that depth plane. The image injection devices 360, 370, 380, 390, 400 may act as light sources for the waveguides and may be utilized to inject image information into the waveguides 270, 280, 290, 300, 310, each configured to disperse incident light across each individual waveguide for output toward the eye 210, as described herein. Light exits output surfaces 410, 420, 430, 440, 450 of the image injection devices 360, 370, 380, 390, 400 and is injected into corresponding input surfaces 460, 470, 480, 490, 500 of the waveguides 270, 280, 290, 300, 310. In some embodiments, each input surface 460, 470, 480, 490, 500 may be an edge of the corresponding waveguide or a portion of a major surface of the corresponding waveguide (i.e., one of the waveguide surfaces that directly faces the world 510 or the viewer's eye 210). It should be understood that a major surface of a waveguide corresponds to a relatively large-area surface of the waveguide between which the thickness of the waveguide extends. In some embodiments, a single beam of light (e.g., a collimated beam) may be launched into each waveguide, outputting a total field of cloned collimated beams that are directed toward the eye 210 at a particular angle (and divergence) corresponding to the depth plane associated with the particular waveguide. In some embodiments, a single one of the image launch devices 360, 370, 380, 390, 400 may be associated with and launch light into multiple (e.g., three) waveguides 270, 280, 290, 300, 310.

[0081] In some embodiments, each of the image input devices 360, 370, 380, 390, 400 is a discrete display that generates image information for input into a corresponding waveguide 270, 280, 290, 300, 310. In some other embodiments, the image input devices 360, 370, 380, 390, 400 are the output of a single multiplexed display that may, for example, send image information via one or more optical conduits (such as fiber optic cables) to each of the image input devices 360, 370, 380, 390, 400. It should be understood that the image information provided by the image input devices 360, 370, 380, 390, 400 may include light of different wavelengths or colors (e.g., different primary colors, as discussed herein).

[0082] In some embodiments, light injected into the waveguides 270, 280, 290, 300, 310 is provided by a light projector system 520, which includes a light module 530, which may include a light emitter such as a light emitting diode (LED). Light from the light module 530 may be directed and modified by a light modulator 540, e.g., a spatial light modulator, via a beam splitter 550. The light modulator 540 may be configured to vary the perceived intensity of the light injected into the waveguides 270, 280, 290, 300, 310 and encode the light with image information. Examples of spatial light modulators include liquid crystal displays (LCDs), including liquid crystal on silicon (LCOS) displays. It should be understood that image injection devices 360, 370, 380, 390, 400 are illustrated diagrammatically, and in some embodiments, these image injection devices may represent different light paths and locations within a common projection system configured to output light into associated ones of waveguides 270, 280, 290, 300, 310. In some embodiments, the waveguides of waveguide assembly 260 may function as ideal lenses, relaying light injected into the waveguides to the user's eye. In this concept, the object may be a spatial light modulator 540, and the image may be an image on a depth plane.

[0083] In some embodiments, the display system 250 may be a scanning fiber display comprising one or more scanning fibers configured to project light in various patterns (e.g., raster scan, spiral scan, Lissajous pattern, etc.) into one or more waveguides 270, 280, 290, 300, 310 and ultimately to the viewer's eye 210. In some embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent a single scanning fiber or a bundle of scanning fibers configured to inject light into one or more waveguides 270, 280, 290, 300, 310. In some other embodiments, the illustrated image injection devices 360, 370, 380, 390, 400 may diagrammatically represent multiple scanning fibers or multiple bundles of scanning fibers, each configured to inject light into an associated one of the waveguides 270, 280, 290, 300, 310. It should be understood that one or more optical fibers may be configured to transmit light from the optical module 530 to one or more waveguides 270, 280, 290, 300, 310. It should be understood that one or more intervening optical structures may be provided between one or more scanning fibers and one or more waveguides 270, 280, 290, 300, 310, for example, to redirect light exiting the scanning fiber into one or more waveguides 270, 280, 290, 300, 310.

[0084] Controller 560 controls the operation of one or more of stacked waveguide assemblies 260, including the operation of image input devices 360, 370, 380, 390, 400, light source 530, and light module 540. In some embodiments, controller 560 is part of local data processing module 140. Controller 560 contains programming (e.g., instructions in a non-transitory medium) that coordinates the timing and provisioning of image information to waveguides 270, 280, 290, 300, 310, for example, according to any of the various schemes disclosed herein. In some embodiments, the controller may be a single integrated device or a distributed system connected by a wired or wireless communication channel. Controller 560 may, in some embodiments, be part of processing module 140 or 150 (FIG. 2).

[0085] Continuing with reference to FIG. 6 , the waveguides 270, 280, 290, 300, and 310 may be configured to propagate light within each individual waveguide by total internal reflection (TIR). Each of the waveguides 270, 280, 290, 300, and 310 may be planar or have another shape (e.g., curved) with major top and bottom surfaces and edges extending between the major top and bottom surfaces. In the illustrated configuration, the waveguides 270, 280, 290, 300, and 310 may each include outcoupling optical elements 570, 580, 590, 600, and 610 configured to extract light from the waveguide by redirecting light propagating within each individual waveguide out of the waveguide and outputting image information to the eye 210. The extracted light may also be referred to as outcoupling light, and the outcoupling optical elements may also be referred to as light extraction optical elements. The extracted beam of light may be output by the waveguide at a location where light propagating within the waveguide strikes the light extraction optical element. The outcoupling optical element 570, 580, 590, 600, 610 may be a grating, for example, including diffractive optical features as discussed further herein. While shown disposed on the bottom major surface of the waveguides 270, 280, 290, 300, 310 for ease of explanation and clarity of the drawings, in some embodiments the outcoupling optical element 570, 580, 590, 600, 610 may be disposed on the top and / or bottom major surfaces and / or directly within the volume of the waveguides 270, 280, 290, 300, 310, as discussed further herein. In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 may be formed within a layer of material that is attached to a transparent substrate and forms the waveguides 270, 280, 290, 300, 310. In some other embodiments, the waveguides 270, 280, 290, 300, 310 may be monolithic pieces of material, and the outcoupling optical elements 570, 580, 590, 600, 610 may be formed on a surface of and / or within that piece of material.

[0086] Continuing with reference to FIG. 6 , as discussed herein, each waveguide 270, 280, 290, 300, 310 is configured to output light and form an image corresponding to a particular depth plane. For example, the waveguide 270 closest to the eye may be configured to deliver collimated light (injected into such waveguide 270) to the eye 210. The collimated light may represent an optical infinity focal plane. The next upper waveguide 280 may be configured to send collimated light that passes through a first lens 350 (e.g., a negative lens) before reaching the eye 210. Such first lens 350 may be configured to generate a slight convex wavefront curvature so that the eye / brain interprets light emerging from the next upper waveguide 280 as emerging from a first focal plane closer inward from optical infinity toward the eye 210. Similarly, the third upper waveguide 290 passes its output light through both the first lens 350 and the second lens 340 before reaching the eye 210. The combined refractive power of the first lens 350 and the second lens 340 may be configured to produce another, increasing amount of wavefront curvature such that the eye / brain interprets the light emerging from the third waveguide 290 as originating from a second focal plane that is closer inward from optical infinity towards the person than was the light from the next upper waveguide 280.

[0087] The other waveguide layers 300, 310 and lenses 330, 320 are similarly configured, with the highest waveguide 310 in the stack sending its output through all of the lenses between it and the eye for a collective focal power representing the focal plane closest to the person. To compensate for the stack of lenses 320, 330, 340, 350 when viewing / interpreting light originating from the world 510 on the other side of the stacked waveguide assembly 260, a compensating lens layer 620 may be placed on top of the stack to compensate for the collective power of the lower lens stacks 320, 330, 340, 350. Such a configuration provides as many perceived focal planes as there are available waveguide / lens pairs. Both the waveguide outcoupling optical elements and the focusing sides of the lenses may be static (i.e., not dynamic or electro-active). In some alternative embodiments, one or both may be dynamic using electro-active features.

[0088] In some embodiments, two or more of the waveguides 270, 280, 290, 300, 310 may have the same associated depth plane. For example, multiple waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth plane, or multiple subsets of waveguides 270, 280, 290, 300, 310 may be configured to output images set at the same depth planes, with one set per depth plane. This may provide the advantage of forming tiled images to provide an extended field of view at those depth planes.

[0089] Continuing with reference to FIG. 6 , the outcoupling optical elements 570, 580, 590, 600, 610 may be configured to redirect light from its respective waveguide and output the light with an appropriate amount of divergence or collimation for a particular depth plane associated with that waveguide. As a result, waveguides with different associated depth planes may have different configurations of outcoupling optical elements 570, 580, 590, 600, 610, which output light with different amounts of divergence depending on the associated depth plane. In some embodiments, the light-extracting optical elements 570, 580, 590, 600, 610 may be volume or surface features, which may be configured to output light at specific angles. For example, the light-extracting optical elements 570, 580, 590, 600, 610 may be volume holograms, surface holograms, and / or diffraction gratings. In some embodiments, features 320, 330, 340, 350 may not be lenses. Rather, they may simply be spacers (e.g., cladding layers and / or structures for forming air gaps).

[0090] In some embodiments, the outcoupling optical elements 570, 580, 590, 600, 610 are diffractive features or "diffractive optical elements" (also referred to herein as "DOEs") that form a diffraction pattern. Preferably, the DOEs have a sufficiently low diffraction efficiency so that only a portion of the light in the beam is deflected toward the eye 210 at each intersection of the DOE, while the remainder continues traveling through the waveguide via TIR. The light carrying the image information is thus split into several related output beams that exit the waveguide at various locations, resulting in a fairly uniform pattern of output emission toward the eye 210 for this particular collimated beam bouncing within the waveguide.

[0091] In some embodiments, one or more DOEs may be switchable between an "on" state in which they actively diffract and an "off" state in which they do not significantly diffract. For example, a switchable DOE may comprise a layer of polymer-dispersed liquid crystal in which microdroplets comprise a diffractive pattern in a host medium, and the refractive index of the microdroplets may be switched to substantially match the refractive index of the host material (in which case the pattern does not significantly diffract incident light), or the microdroplets may be switched to a refractive index that does not match that of the host medium (in which case the pattern actively diffracts incident light).

[0092] In some embodiments, a camera assembly 630 (e.g., a digital camera, including visible and infrared light cameras) may be provided to capture images of the eye 210 and / or tissue surrounding the eye 210, for example, to detect user input and / or monitor the physiological state of the user. As used herein, a camera may be any image capture device. In some embodiments, the camera assembly 630 may include an image capture device and a light source that projects light (e.g., infrared light) onto the eye, which may then be reflected by the eye and detected by the image capture device. In some embodiments, the camera assembly 630 may be mounted on the frame 80 ( FIG. 2 ) and may be in electrical communication with processing modules 140 and / or 150, which may process image information from the camera assembly 630. In some embodiments, one camera assembly 630 may be utilized for each eye, monitoring each eye separately.

[0093] 7, an example of an output beam output by a waveguide is shown. While one waveguide is illustrated, it should be understood that other waveguides in waveguide assembly 260 (FIG. 6) may function similarly, and that waveguide assembly 260 includes multiple waveguides. Light 640 is launched into waveguide 270 at input surface 460 of waveguide 270 and propagates within waveguide 270 by TIR. At the point where light 640 impinges on DOE 570, a portion of the light exits the waveguide as output beam 650. Output beam 650 is illustrated as being approximately parallel, but may be redirected to propagate to eye 210 at an angle (e.g., forming a diverging output beam), as discussed herein and depending on the depth plane associated with waveguide 270. It should be understood that a nearly collimated exit beam may refer to a waveguide with outcoupling optics that outcouples light to form an image that appears to be set at a depth plane at a large distance (e.g., optical infinity) from the eye 210. Other waveguides or other sets of outcoupling optics may output a more divergent exit beam pattern, which would require the eye 210 to accommodate to a closer distance and focus on the retina, and would be interpreted by the brain as light from a distance closer to the eye 210 than optical infinity.

[0094] In some embodiments, a full-color image may be formed at each depth plane by overlaying images in each of the primary colors, for example, three or more primary colors. FIG. 8 illustrates an example of a stacked waveguide assembly, with each depth plane including an image formed using multiple different primary colors. The illustrated embodiment shows depth planes 240a-240f, but more or fewer depths are also contemplated. Each depth plane may have three or more primary color images associated with it, including a first image in a first color G, a second image in a second color R, and a third image in a third color B. Different depth planes are indicated in the diagram by different numbers in diopters following the letters G, R, and B. By way of example only, the number following each of these letters indicates the diopter (1 / m), i.e., the inverse distance of the depth plane from the viewer, and each box in the diagram represents an individual primary color image. In some embodiments, the exact locations of the depth planes for the different primary colors may be varied to account for differences in the eye's focusing of light of different wavelengths. For example, different primary color images for a given depth plane may be placed on depth planes corresponding to different distances from the user. Such an arrangement may increase visual acuity and user comfort and / or reduce chromatic aberration.

[0095] In some embodiments, light for each primary color may be output by a single dedicated waveguide, such that each depth plane may have multiple waveguides associated with it. In such embodiments, each box in the diagram containing the letter G, R, or B may be understood to represent an individual waveguide, and three waveguides may be provided per depth plane, resulting in three primary color images per depth plane. While the waveguides associated with each depth plane are shown adjacent to each other in this drawing for ease of illustration, it should be understood that in a physical device, the waveguides may all be arranged in a stack with one waveguide per level. In some other embodiments, multiple primary colors may be output by the same waveguide, such that, for example, only a single waveguide may be provided per depth plane.

[0096] 8, in some embodiments, G is green, R is red, and B is blue. In some other embodiments, other colors associated with other wavelengths of light, including magenta and cyan, may be used in addition to or replace one or more of red, green, or blue.

[0097] It should be understood that references throughout this disclosure to a given color of light are understood to encompass light of one or more wavelengths within the range of wavelengths of light that are perceived by a viewer as that given color. For example, red light may include one or more wavelengths of light that are within the range of about 620-780 nm, green light may include one or more wavelengths of light that are within the range of about 492-577 nm, and blue light may include one or more wavelengths of light that are within the range of about 435-493 nm.

[0098] In some embodiments, light source 530 (FIG. 6) may be configured to emit light at one or more wavelengths outside the range of a viewer's visual perception, e.g., infrared and / or ultraviolet wavelengths. Additionally, the waveguide incoupling, outcoupling, and other light redirecting structures of display 250 may be configured to direct and emit this light from the display toward the user's eye 210, e.g., for imaging and / or user stimulation applications.

[0099] Referring now to FIG. 9A , in some embodiments, light impinging on a waveguide may need to be redirected to incoupling the light into the waveguide. An incoupling optical element may be used to redirect and incoupling the light into its corresponding waveguide. FIG. 9A illustrates a cross-sectional side view of an example of a plurality or set 660 of stacked waveguides, each including an incoupling optical element. The waveguides may each be configured to output light of one or more different wavelengths or one or more different wavelength ranges. Stack 660 may correspond to stack 260 ( FIG. 6 ), and the illustrated waveguides of stack 660 may correspond to a portion of multiple waveguides 270, 280, 290, 300, 310, although it should be understood that light from one or more of image injection devices 360, 370, 380, 390, 400 is injected into the waveguide from a location requiring the light to be redirected for incoupling.

[0100] The illustrated set 660 of stacked waveguides includes waveguides 670, 680, and 690. Each waveguide includes an associated internal coupling optical element (which may also be referred to as the light input area on the waveguide), for example, internal coupling optical element 700 is disposed on a major surface (e.g., the top major surface) of waveguide 670, internal coupling optical element 710 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and internal coupling optical element 720 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some embodiments, one or more of internal coupling optical elements 700, 710, 720 may be disposed on the bottom major surface of an individual waveguide 670, 680, 690 (particularly, one or more internal coupling optical elements are reflective polarizing optical elements). As shown, the internal coupling optical elements 700, 710, 720 may be disposed on the upper major surface of the respective waveguide 670, 680, 690 (or on top of the next lower waveguide), and in particular, the internal coupling optical elements are transmissive turning optical elements. In some embodiments, the internal coupling optical elements 700, 710, 720 may be disposed within the body of the respective waveguide 670, 680, 690. In some embodiments, as discussed herein, the internal coupling optical elements 700, 710, 720 are wavelength selective, such that they selectively redirect one or more wavelengths of light while transmitting other wavelengths of light. While illustrated on one side or corner of the respective waveguide 670, 680, 690, it should be understood that the internal coupling optical elements 700, 710, 720 may be disposed within other areas of the respective waveguide 670, 680, 690 in some embodiments.

[0101] As shown, the in-coupling optical elements 700, 710, 720 may be laterally offset from one another. In some embodiments, each in-coupling optical element may be offset to receive light without that light passing through another in-coupling optical element. For example, each in-coupling optical element 700, 710, 720 may be configured to receive light from different image input devices 360, 370, 380, 390, and 400, as shown in FIG. 6 , and may be separated (e.g., laterally spaced) from the other in-coupling optical elements 700, 710, 720 so as to receive substantially no light from others of the in-coupling optical elements 700, 710, 720.

[0102] Each waveguide also includes an associated optically dispersive element, for example, optically dispersive element 730 is disposed on a major surface (e.g., the top major surface) of waveguide 670, optically dispersive element 740 is disposed on a major surface (e.g., the top major surface) of waveguide 680, and optically dispersive element 750 is disposed on a major surface (e.g., the top major surface) of waveguide 690. In some other embodiments, optically dispersive elements 730, 740, 750 may be disposed on the bottom major surfaces of the associated waveguides 670, 680, 690, respectively. In some other embodiments, the optically dispersive elements 730, 740, 750 may be disposed on both the top and bottom major surfaces of the associated waveguides 670, 680, 690, respectively, or the optically dispersive elements 730, 740, 750 may be disposed on different ones of the top and bottom major surfaces in different associated waveguides 670, 680, 690, respectively.

[0103] Waveguides 670, 680, 690 may be spaced apart and separated, for example, by gas, liquid, and / or solid layers of material. For example, as shown, layer 760a may separate waveguides 670 and 680, and layer 760b may separate waveguides 680 and 690. In some embodiments, layers 760a and 760b are formed from a low refractive index material (i.e., a material having a lower refractive index than the material forming the immediately adjacent waveguides 670, 680, 690). Preferably, the refractive index of the material forming layers 760a, 760b is 0.05 or more or 0.10 or less compared to the refractive index of the material forming waveguides 670, 680, 690. Advantageously, the lower refractive index layers 760a, 760b may function as cladding layers that promote total internal reflection (TIR) ​​of light through the waveguides 670, 680, 690 (e.g., TIR between the top and bottom major surfaces of each waveguide). In some embodiments, the layers 760a, 760b are formed from air. Although not shown, it should be understood that the top and bottom of the illustrated set of waveguides 660 may include immediate cladding layers.

[0104] Preferably, for ease of manufacturing and other considerations, the materials forming waveguides 670, 680, 690 are similar or the same, and the materials forming layers 760a, 760b are similar or the same. In some embodiments, the materials forming waveguides 670, 680, 690 may differ between one or more waveguides, and / or the materials forming layers 760a, 760b may differ while still maintaining the various refractive index relationships discussed above.

[0105] 9A, light rays 770, 780, 790 enter the set of waveguides 660. It should be understood that light rays 770, 780, 790 may be injected into the waveguides 670, 680, 690 by one or more image injection devices 360, 370, 380, 390, 400 (FIG. 6).

[0106] In some embodiments, light rays 770, 780, 790 have different properties, e.g., different wavelengths or different wavelength ranges, which may correspond to different colors. Each of the incoupling optical elements 700, 710, 720 deflects incident light such that the light propagates through a respective one of the waveguides 670, 680, 690 by TIR. In some embodiments, each of the incoupling optical elements 700, 710, 720 selectively deflects one or more particular wavelengths of light while transmitting other wavelengths to the underlying waveguide and associated incoupling optical element.

[0107] For example, in-coupling optical element 700 may be configured to selectively deflect light ray 770 having a first wavelength or wavelength range while transmitting light rays 1242 and 1244 having different second and third wavelengths or wavelength ranges, respectively. Transmitted light ray 780 impinges on and is deflected by in-coupling optical element 710, which is configured to selectively deflect light of the second wavelength or wavelength range. Light ray 790 is deflected by in-coupling optical element 720, which is configured to selectively deflect light of the third wavelength or wavelength range.

[0108] 9A , the deflected light rays 770, 780, 790 are deflected to propagate through the corresponding waveguides 670, 680, 690. That is, the in-coupling optical element 700, 710, 720 of each waveguide deflects the light into its corresponding waveguide 670, 680, 690, in-coupling the light into the corresponding waveguide. The light rays 770, 780, 790 are deflected at an angle that causes the light to propagate through the respective waveguides 670, 680, 690 by TIR. The light rays 770, 780, 790 propagate through the respective waveguides 670, 680, 690 by TIR until they impinge on the waveguide's corresponding optical dispersive element 730, 740, 750.

[0109] 9B, a perspective view of the multiple stacked waveguide embodiment of FIG. 9A is illustrated. As previously described, in-coupled light rays 770, 780, 790 are deflected by in-coupling optical elements 700, 710, 720, respectively, and then propagate by TIR within waveguides 670, 680, 690, respectively. Light rays 770, 780, 790 then impinge on optically dispersive elements 730, 740, 750, respectively. Optically dispersive elements 730, 740, 750 deflect light rays 770, 780, 790 to propagate toward out-coupling optical elements 800, 810, 820, respectively.

[0110] In some embodiments, the optically dispersive elements 730, 740, 750 are orthogonal pupil expanders (OPEs). In some embodiments, the OPEs deflect or disperse light into the out-coupling optical elements 800, 810, 820, and in some embodiments, may also increase the beam or spot size of this light as it propagates into the out-coupling optical elements. In some embodiments, the optically dispersive elements 730, 740, 750 may be omitted, and the in-coupling optical elements 700, 710, 720 may be configured to deflect light directly into the out-coupling optical elements 800, 810, 820. For example, with reference to FIG. 9A , the optically dispersive elements 730, 740, 750 may be replaced with the out-coupling optical elements 800, 810, 820, respectively. In some embodiments, the outcoupling optical elements 800, 810, 820 are exit pupils (EPs) or exit pupil expanders (EPEs) that direct light toward the viewer's eye 210 ( FIG. 7 ). It should be understood that an OPE may be configured to increase the size of the eyebox in at least one axis, and that an EPE may increase the eyebox in an axis that intersects (e.g., is perpendicular to) the axis of the OPE. For example, each OPE may be configured to redirect a portion of the light striking the OPE to an EPE in the same waveguide, while allowing the remaining portion of the light to continue propagating down the waveguide. Upon striking the OPE, again, another portion of the remaining light is redirected to the EPE, and the remainder of that portion continues to propagate further down the waveguide, etc. Similarly, upon striking the EPE, a portion of the impinging light is directed out of the waveguide toward the user, and the remaining portion of that light continues to propagate through the waveguide until it again strikes an EP, at which point another portion of the impinging light is directed out of the waveguide, etc. As a result, a single beam of internally coupled light may be "replicated" each time a portion of that light is redirected by an OPE or EPE, thereby forming a cloned beam field of light, as shown in Figure 6. In some embodiments, the OPE and / or EPE may be configured to modify the size of the beam of light.

[0111] 9A and 9B, in some embodiments, a waveguide set 660 includes, for each primary color, waveguides 670, 680, 690, in-coupling optical elements 700, 710, 720, optically dispersive elements (e.g., OPEs) 730, 740, 750, and out-coupling optical elements (e.g., EPs) 800, 810, 820. The waveguides 670, 680, 690 may be stacked with an air gap / cladding layer between each one. The in-coupling optical elements 700, 710, 720 redirect or deflect incident light into their respective waveguides (with different in-coupling optical elements receiving light of different wavelengths). The light then propagates at an angle that will result in TIR within the individual waveguides 670, 680, 690. In the example shown, light ray 770 (e.g., blue light) is deflected by the first in-coupling optical element 700 in the manner described above, then continues bouncing back down the waveguide, interacting with an optically dispersive element (e.g., OPE) 730 and then an out-coupling optical element (e.g., EP) 800. Light rays 780 and 790 (e.g., green and red light, respectively) pass through waveguide 670, with light ray 780 impinging on and being deflected by in-coupling optical element 710. Light ray 780 will then, via TIR, bounce back down waveguide 680 to its optically dispersive element (e.g., OPE) 740 and then to the out-coupling optical element (e.g., EP) 810. Finally, light ray 790 (e.g., red light) passes through waveguide 690 and impinges on the optically in-coupling optical element 720 of waveguide 690. The light in-coupling optical element 720 deflects the light ray 790 so that it propagates by TIR to the light dispersive element (e.g., OPE) 750 and then by TIR to the out-coupling optical element (e.g., EP) 820. The out-coupling optical element 820 then finally out-couples the light ray 790 to a viewer, who also receives the out-coupled light from the other waveguides 670, 680.

[0112] FIG. 9C illustrates a top-down plan view of an example of the multiple stacked waveguides of FIGS. 9A and 9B. As shown, waveguides 670, 680, 690 may be vertically aligned, along with each waveguide's associated optically dispersive elements 730, 740, 750 and associated out-coupling optical elements 800, 810, 820. However, as discussed herein, the in-coupling optical elements 700, 710, 720 are not vertically aligned. Rather, the in-coupling optical elements are preferably non-overlapping (e.g., laterally spaced apart, as seen in the top-down view). As discussed further herein, this non-overlapping spatial arrangement facilitates the injection of light from different sources into different waveguides on a one-to-one basis, thereby allowing a specific light source to be uniquely coupled to a specific waveguide. In some embodiments, arrays including non-overlapping, spatially separated in-coupling optical elements may be referred to as shifted-pupil systems, and the in-coupling optical elements in these arrays may correspond to sub-pupils.

[0113] 10 , a cross-sectional side view of an exemplary optical structure 1400 is shown, comprising a metasurface 1418 formed by a plurality of nanostructures 1420 and an antireflective coating 1430 disposed directly over the nanostructures 1420, according to some embodiments. The metasurface 1418 and antireflective coating 1430 may be disposed on an optically transmissive substrate 1410. In some embodiments, as shown, the antireflective coating 1430 fills the spaces between the nanostructures 1420 such that no air or other material is disposed between the nanostructures 1420 and the antireflective coating 1430, at least across the majority of the extent of the metasurface 1418. The antireflective coating 1430 may be optically transmissive or substantially transmissive to light.

[0114] In some embodiments, the antireflective coating 1430 has a substantially flat upper surface 1430a. The antireflective coating 1430 may act as a planarizing layer for the underlying non-uniform topology of the nanostructures 1420. In some embodiments, the upper surface 1430a of the antireflective coating 1430 may be substantially parallel to the substantially horizontal plane defined by the upper surfaces 1420a of the nanostructures 1420.

[0115] The thickness 1422 of the antireflective coating 1430 may be defined as the distance from the top surface 1420a of the nanostructures 1420 to the upper surface of the antireflective coating 1430. In some embodiments, the thickness 1422 may be in a range from about 10 nm to about 2 microns. In some embodiments, the thickness 1422 may be from about 20 nm to about 1 micron. In some embodiments, the thickness 1422 may be from about 25 nm to about 500 nm, from about 30 nm to about 250 nm, from about 40 nm to about 100 nm, and from about 45 nm to about 55 nm. In some embodiments, the thickness 1422 may be about 50 nm. In some embodiments, the thickness 1422 may be greater than the height of the nanostructures 1420, where the height of the nanostructures 1420 is the distance from the bottom of the nanostructures 1420 to the top surface 1420a.

[0116] Without being bound by theory, it is believed that the antireflective coating 1430 may provide an impedance match between the overlying medium (e.g., air) and one or both of the nanostructures 1420 and substrate 1410, reducing the occurrence of reflections. It is also believed that the antireflective coating 1430 may cause destructive interference between light reflected from the top surface 1430 a of the antireflective coating and the bottom surface 1430 b of the antireflective coating and / or light backscattered from the surface of the nanostructures 1420 and / or the surface of the substrate 1410. It is believed that this interference leads to a reduction or elimination in the amount of light perceived as reflected from the optical structure 1400. In some embodiments, the ability of the antireflective coating 1430 to reduce or eliminate light reflected from the optical structure 1400 may depend on the thickness of the antireflective coating 1430 and the wavelength of the light impinging on the antireflective coating 1430. Preferably, thickness 1422 is selected relative to the refractive index and dimensions of nanostructures 1420 and the wavelength of light for which destructive interference is desired, as described above, to provide destructive interference.

[0117] The antireflective coating 1430 may comprise an optically transmissive material having a refractive index lower than the refractive index of the nanostructures 1420 but higher than the refractive index of the medium or material directly overlying and interfacing with the antireflective coating 1430. For example, the medium overlying and interfacing with the antireflective coating 1430 may be air. In some embodiments, the antireflective coating 1430 may have a refractive index of about 1.2 to about 2.0, about 1.2 to about 1.7, about 1.3 to about 1.6, or about 1.4 to about 1.5. In some embodiments, the antireflective coating 1430 may have a refractive index of about 1.45. In some embodiments, the refractive index of the antireflective coating 1430 may also be lower than the refractive index of the substrate 1410. It should be understood that in some embodiments, the lower refractive index of the antireflective coating 1430 compared to the substrate 1410 facilitates TIR of light within the substrate 1410, and the higher refractive index of the antireflective coating 1430 compared to the medium covering the coating 1430 facilitates passage of light to the metasurface 1418 for internal coupling into the substrate 1410.

[0118] 10 , to reduce potential reflections caused by interfaces between additional materials, the antireflective coating 1430 may follow the contours of the nanostructures 1420 such that, over all or substantially all of the area where the metasurface is disposed, substantially no air or other material is present between the nanostructures 1420 and the antireflective coating 1430. In some embodiments, as shown, the antireflective coating 1430 is disposed directly on the optical structure 1400 such that the antireflective coating 1430 encapsulates the nanostructures 1420 above the surface of the substrate 1410.

[0119] As discussed herein, the antireflective coating 1430 preferably comprises an optically transmissive material. By way of example, the optically transmissive material may be an optically transmissive organic material, such as a transparent polymer. In some embodiments, the antireflective coating 1430 may comprise a resist material, such as a photoresist material. Non-limiting examples of photoresist include positive resist and negative resist. In some embodiments, the antireflective coating 1430 may comprise a UV photoresist, an EUV photoresist, or a DUV photoresist.

[0120] It should be understood that the antireflective coating 1430 may be formed on the nanostructures 1420 by a variety of deposition processes. In some embodiments, the antireflective coating 1430 may be applied to the nanostructures 1420 as a liquid, whereby the liquid forms the antireflective coating 1430. For example, the antireflective coating 1430 may be deposited on the nanostructures 1420 as a liquid by spin coating. In some embodiments, the antireflective coating 1430 may be deposited on the nanostructures 1420 using gas-phase precursors in a vapor deposition process, such as a chemical vapor deposition (CVD) process and atomic layer deposition (ALD).

[0121] In some embodiments, the anti-reflective coating 1430 may reduce the amount of incident light reflected by the optical structure 1400 operating in a transmissive mode by about 50%, 75%, 85%, 90%, 95%, 99%, or more, compared to a substantially similar optical structure without the anti-reflective coating 1430. In some embodiments, the anti-reflective coating may achieve such a reduction in reflected light over a wide range of angles of incidence: from -10° to 10°, from -20° to 20°, from -30° to 30°, from -40° to 40°, from -50° to 50°, or more.

[0122] The metasurface 1418, comprising the plurality of nanostructures 1420, may be configured to manipulate light, such as for beam steering, wavefront shaping, wavelength and / or polarization separation, and combining different wavelengths and / or polarizations. Preferably, the light is visible light, having a wavelength in the range of 350 nm to 800 nm. In some embodiments, the metasurface on which the anti-reflective coating is disposed may comprise nanostructures having a size and periodicity less than the wavelength of visible light. It should be understood that in some embodiments, the metasurface 1418 selectively redirects some wavelengths of light while allowing other wavelengths of light to pass without being redirected. While such properties are typically engineered using structures on the micron scale (e.g., photonic crystal fibers or distributed Bragg reflectors), various embodiments herein include nanoscale (e.g., 10-100 times smaller) geometries to provide selective redirection of light within the visible portion of the electromagnetic spectrum.

[0123] As an example, the metasurface 1418 may operate in a transmission mode, where light enters the metasurface from a first side of the metasurface 1418, propagates through the body of the metasurface 1418, and then propagates away from the metasurface 1418 on the opposite side of the metasurface 1418. The light propagates away from the metasurface 1418 in a direction different from the direction of incidence of the light on the first side. In some embodiments, the antireflective coating 1430 may reduce or eliminate the amount of light reflected from the metasurface 1418 compared to a metasurface 1418 without the antireflective coating 1430. In some embodiments, the antireflective coating 1430 may not substantially reduce or have no effect on the amount of light propagating through and away from the metasurface 1418 compared to a metasurface 1418 without the antireflective coating 1430.

[0124] In some embodiments, the substrate 1410 supporting the metasurface 1418 on which the anti-reflective coating 1430 is disposed may be a waveguide, and the waveguide may be used to form a direct-view or eyepiece display device configured to receive input image information and generate an output image in the form of light encoded with the image information based on the input image information. These devices may be wearable and, in some embodiments, constitute eyewear or may be the display devices described herein with respect to FIGS. 1-9C . In some embodiments, the input image information received by the waveguide may be encoded into multiplexed light streams of different wavelengths (e.g., red, green, and blue light) that are internally coupled into one or more waveguides. The internally coupled light may propagate through the waveguide due to total internal reflection. The internally coupled light may be externally coupled (or output) from the waveguide by one or more external coupling optical elements, as described above with respect to FIGS. 9A-9C .

[0125] In some embodiments, the metasurface 1418, upon which the anti-reflective coating 1430 is conformally disposed, may be the in-coupling optical element, the out-coupling optical element, and / or the light-dispersing element of the waveguide. The compactness and planarity of the metasurface 1418 and the anti-reflective coating 1430 enable compact waveguides and compact waveguide stacks, where multiple waveguides form a stack. Additionally, the metasurface 1418 may be configured to provide high precision when in-coupling and / or out-coupling light, which may provide high image quality. For example, high selectivity may reduce channel crosstalk in configurations where a full-color image is formed by simultaneously outputting light of different colors or wavelengths, while the anti-reflective coating 1430 may reduce residual images.

[0126] It should be understood that the nanostructures 1420 may have various sizes and be arranged in various orientations relative to one another to form the metasurface 1418 for various applications. For example, as discussed herein, the nanostructures 1420 may be arranged to form a grating, such as an asymmetric or asymmetric grating. In some embodiments, the metasurface 1418 may be formed from nanostructures 1420 that are multi-level or multi-tiered. For example, the nanostructures 1420 may be relatively wide on a first level and relatively narrow on a second level. In some embodiments, the metasurface 1418 may be formed on a single level and have a substantially constant width on that level. Examples of metasurfaces that may be utilized as metasurface 1418 are described in U.S. patent application Ser. No. 15 / 342,033, filed Nov. 2, 2016 (Attorney Docket No. MLEAP.027A), U.S. Provisional Application Ser. No. 62 / 333,067, filed May 6, 2016 (Attorney Docket No. MLEAP.066PR), entitled "Diffraction Gratings Formed by Metasurfaces Having Differently Oriented Nanobeams," and U.S. Provisional Application Ser. No. 62 / 451,608, filed Jan. 27, 2017 (Attorney Docket No. MLEAP.092PR), entitled "Diffraction Gratings Formed by Metasurfaces Having Differently Oriented Nanobeams," and U.S. Provisional Application Ser. No. 62 / 451,608, filed Jan. 27, 2017 (Attorney Docket No. MLEAP.092PR), entitled "Diffraction Gratings Based on Metasurfaces Having Asymmetric Optical No. 62 / 451,615, filed January 27, 2017, entitled "META-RESISTANT ELEMENTS," and Attorney Docket No. MLEAP.103PR, each of which is incorporated herein by reference. It should be understood that the nanostructures 1420 disclosed herein may correspond to the protrusions, nanobeams, etc. described in these applications. In some embodiments, the optical structure 1400 may be any metasurface comprising a plurality of nanostructures known in the art or developed in the future.

[0127] Examples of different configurations of nanostructure 1420 are described below. It should be understood that for clarity of description, the nanostructures discussed below may have different reference numbers than 1420. However, it should be understood that the various nanostructures (1520, 1620) described below correspond to nanostructure 1420 of FIG. 10.

[0128] 11A , a top-down view of an exemplary optical structure 1500 comprising a metasurface 1518 with nanostructures 1520 forming an asymmetric Pancharatnam Berry phase optical element (PBOE), which may be advantageous for, among other things, light steering, according to some embodiments, is shown. A substrate 1410 underlies the nanostructures 1520. In some embodiments, the substrate 1410 may be an optically transparent substrate, such as a waveguide.

[0129] 11B , a perspective view of an exemplary optical element 1500 comprising an asymmetric Pancharatnam Berry phase optical element (PBOE) and including an antireflective coating 1430 is illustrated, according to some embodiments. As described herein, the antireflective coating 1430 follows the contours of the nanostructures 1520 such that substantially no air or other material exists between the nanostructures 1520 and the antireflective coating 1430. Further, as described herein, the antireflective coating 1430 may have a substantially flat upper surface 1430 a. The antireflective coating 1430 may function as a planarizing layer for the underlying non-uniform topology of the nanostructures 1520. In some embodiments, the upper surface 1430 a of the antireflective coating 1430 may be substantially parallel to a substantially horizontal plane defined by the upper surfaces (not shown) of the nanostructures 1520. The thickness 1522 of the antireflective coating 1430 may be defined as the distance from the top surface of the nanostructures 1520 to the upper surface 1430a of the antireflective coating 1430. In some embodiments, the thickness 1522 may be in a range from about 10 nm to about 2 microns. In some embodiments, the thickness 1522 may be from about 20 nm to about 1 micron. In some embodiments, the thickness 1522 may be from about 25 nm to about 500 nm, from about 30 nm to about 250 nm, from about 40 nm to about 100 nm, and from about 45 nm to about 55 nm. In some embodiments, the thickness 1522 may be about 50 nm. In some embodiments, the thickness 1522 may be selected based on the wavelength of light that the metasurface is configured to redirect and is therefore expected to impinge on the antireflective coating 1430. Preferably, thickness 1522 is selected to provide destructive interference between light reflected from the top and bottom surfaces of antireflective coating 1430, respectively, the bottom surface (not shown) being the surface of the antireflective coating that forms an interface with the top surface of nanostructure 1520.

[0130] FIG. 11C is a plot of transmission and reflection as a function of the angle of incidence of light for an optical structure having the general structure described with reference to FIGS. 11A-11B. Diffracted transmitted light of various orders is indicated by "T," and reflected light is indicated by "R." In this example, the antireflective coating 1430 is an optically transmissive photoresist having a refractive index of approximately 1.45, which is lower than the refractive index of the nanostructures 1520 and lower than the refractive index of the substrate 1410, which is formed from polysilicon, which is approximately 1.77. The thickness 1522 of the antireflective coating 1430 is approximately 50 nm, and air forms an interface with the top surface of the antireflective coating 1430.

[0131] As can be seen from the plot, the percentage of incident light reflected from optical structure 1500 remains below approximately 2% over a wide range of angles of incidence, from greater than −20° to greater than 20°. By comparison, the percentage of light reflected from a substantially similar metasurface 1518 without an antireflective coating was determined to be approximately 10% (not shown) over the same range of angles of incidence. Thus, in this embodiment, antireflective coating 1430 provides approximately an 80% reduction in the amount of light reflected from metasurface 1518 compared to a substantially similar metasurface 1518 without antireflective coating 1430.

[0132] Meanwhile, the percentage of light incident on metasurface 1518 with antireflective coating 1430 that undergoes first-order diffraction for angles suitable for TIR (T1) is approximately 42% for an angle of incidence of 0° and remains at approximately this level over angles of incidence from about −10° to about 10°. Advantageously, the amount of incident light diffracted at angles suitable for TIR is substantially the same as for a substantially similar metasurface 1518 without antireflective coating 1430. Thus, metasurface 1518 with antireflective coating 1430 may be used as an optical element 1500 as described herein, e.g., an incoupling optical element, while reducing the amount of light reflected without a substantial reduction in the amount of light incoupling, thereby reducing or eliminating potential afterimage images in a display device in which the optical element is incorporated.

[0133] Referring now to FIG. 12A , a cross-sectional perspective view of an exemplary optical element 1600 is shown, comprising a metasurface 1618 and an antireflective coating 1430. The metasurface 1618 comprises an asymmetric diffraction grating formed by nanostructures 1620 with different widths. FIG. 12B illustrates a cross-sectional side view of the optical element 1600 of FIG. 12A . In this example, the substrate 1410 comprises sapphire, having a refractive index of approximately 1.77. The nanostructures 1620 comprise amorphous silicon. The antireflective coating 1430 may comprise an optically transmissive photoresist, having a material refractive index of approximately 1.45, and in some embodiments, may be conformally applied to the asymmetric diffraction grating 1618 by spin coating. The thickness 1622 of the antireflective coating 1430, which is the distance from the top surface 1620 a of the nanostructures 1620 to the top surface 1430 a of the antireflective coating 1430, is approximately 50 nm.

[0134] 12A-12B。 As can be seen from the plot, the percentage of incident light reflected from the optical element 1600 with the anti-reflective coating 1430 remains below about 2% over a wide range of angles of incidence, from greater than -30° to greater than 30°. The percentage of light reflected from the optical element 1600 with the anti-reflective coating 1430 is about 0 over angles of incidence from about -15° to about 15°.

[0135] In comparison, the percentage of light reflected from a substantially similar optical element 1600 without the anti-reflective coating 1430 is about 15% (not shown) over the same range of angles of incidence. Thus, in this embodiment, the anti-reflective coating 1430 provides about an 87% reduction in the amount of light reflected from the optical element 1600 compared to a substantially similar optical element 1600 without the anti-reflective coating 1430.

[0136] On the other hand, the percentage of light incident on optical element 1600 with antireflective coating 1430 that undergoes first-order diffraction for TIR (T1) is greater than about 30% over angles of incidence from about −30° to about 20°. Advantageously, the amount of incident light diffracted for TIR for optical element 1600 with antireflective coating 1430 is substantially the same as the amount of light diffracted for TIR for a substantially similar optical element 1600 without antireflective coating 1430. Thus, optical element 1600 with antireflective coating 1430 may be used as an optical element as described herein, e.g., an incoupling optical element, without a substantial reduction in the amount of incoupling light, while reducing the amount of reflected light, thereby reducing or eliminating potential afterimages, as discussed herein.

[0137] It should be understood that the metal surfaces and nanostructures disclosed herein may be formed by patterning, such as by patterning with lithography and etching. In some embodiments, metasurfaces and nanostructures may be patterned using nanoimprinting, thereby avoiding costly lithography and etching processes. Once the nanostructures are patterned, any mask material may, in some embodiments, be removed, and an antireflective coating 1430 may be applied to, deposited over, or formed on the metasurface as described herein. In some other embodiments, the mask material itself may be utilized as the antireflective coating. Figures 13A-13D and 14A-14D illustrate example process flows for forming optical structures with antireflective coatings.

[0138] 13A-13D illustrate cross-sectional views of intermediate structures 1700A-1700D, respectively, at various stages of fabrication of optical elements 1400, 1500, 1600 having metasurfaces 1418, 1518, 1618 using lithography and etching, according to some embodiments. Referring to intermediate structure 1700A of FIG. 13A, the method includes providing a substrate 1410 having a surface 1410S suitable for forming metasurfaces 1418, 1518, 1618 thereon. Substrate 1410 includes an optically transmissive material having a refractive index n2 and various other material attributes, as described above with reference to FIG. 10. The method additionally includes providing a substrate 1410 having a surface 1410S suitable for forming metasurfaces 1418, 1518, 1618 thereon. 1bulkThe method includes forming a high-refractive index layer 1411 having a thickness of 1 / 2 mm or less. The high-refractive index layer 1411, when patterned, is suitable for forming one or more nanostructures 1420, 1520, 1620, as described above with reference to FIGS. 10-12 . The high-refractive index layer 1411, according to some embodiments, may be deposited using any suitable technique, such as chemical vapor deposition (CVD), including plasma-based CVD processes such as plasma-enhanced chemical vapor deposition (PECVD) and thermal-based CVD processes such as low-pressure chemical vapor deposition (LPCVD). The high-refractive index layer 1411 may also be deposited using physical vapor deposition (PVD), evaporation, and atomic layer deposition, among other techniques. The method additionally includes forming a mask layer 1431A over the high-refractive index layer 1411. The mask layer 1431A may be formed from or include one or more layers of material suitable for providing a template for subsequent etching of the underlying high-refractive index layer 1411. In some embodiments, the mask layer 1431A may be photoresist, which may be spin-coated and then post-baked. In some other embodiments, the mask layer 1431A may include multiple layers, including a hard mask layer formed on the high refractive index layer 1411 and a photoresist layer formed on the hard mask layer. The hard mask layer may be included, for example, when the photoresist layer may not provide sufficient etch selectivity during subsequent etch pattern transfer to the underlying high refractive index layer 1411. The hard mask layer may also serve as an anti-reflective coating to minimize reflections during subsequent exposure processes. In some embodiments, the hard mask layer may be a film deposited by either a spin-coated polymer or deposition technique for depositing the high refractive index layer 1411. When included, the hard mask layer may provide better etch selectivity than the overlying photoresist layer. In some embodiments, the photoresist may be a positive photoresist or a negative photoresist.A positive photoresist is a type of photoresist in which the portions of the photoresist exposed to light become soluble in a photoresist developer, while a negative resist is a type of photoresist in which the portions of the photoresist exposed to light become insoluble in a photoresist developer.

[0139] In some embodiments, the photoresist and / or hard mask layer may be formed from a silicon or silicon oxide containing material that may have sufficient etch selectivity to the high refractive index layer 1411 such that the photoresist and / or hard mask layer remains relatively intact through etching of the underlying high refractive index layer 1411. In these embodiments, the silicon or silicon oxide containing photoresist and / or hard mask layer may remain on top of the one or more nanostructures 1420, 1520, 1620 after patterning, as described above with reference to Figures 10-12.

[0140] Referring to intermediate structure 1700B in FIG. 13B , after deposition and post-deposition bake, the method includes patterning the photoresist layer of mask layer 1431 by selectively exposing portions of the photoresist to a pattern of light. Exposure to light, e.g., coherent UV light or an electron beam, causes chemical changes, e.g., polymer cross-linking, in the photoresist, which allows the exposed portions of the photoresist to be selectively removed by a developer solution for positive photoresist, or the unexposed portions of the photoresist to be selectively removed by a developer solution for negative photoresist. Upon selective removal, the resulting patterned mask photoresist remains on high refractive index layer 1411, thereby serving as a template for subsequent patterning of the underlying hard mask layer, if included, e.g., by etching. The resulting intermediate structure 1700C shows patterned mask layer 1411, which includes patterned photoresist and, optionally, a patterned hard mask layer, if included.

[0141] Referring to intermediate structure 1700C of FIG. 13C , patterned mask layer 1431 may be used as a template to etch underlying high-index layer 1411 into one or more nanostructures 1420, 1520, 1620. It should be understood that nanostructures 1420, 1520, 1620 may be configured as desired based on the desired properties of the resulting metasurface. In some embodiments, nanostructures 1420, 1520, 1620 may include features extending in a first lateral direction (e.g., the y-direction) and a plurality of second nanostructures 1420, 1520, 1620 extending in a second direction (e.g., the x-direction), as described in more detail above with reference to FIGS. 10-12 . In various embodiments, high-index layer 1411 may be etched, for example, anisotropically dry etched. The etching process employed may have suitable selectivity to mask layer 1431 and / or substrate 1410 such that portions of high refractive index layer 1411 are removed without prematurely removing mask layer 1431 and / or undesirably damaging exposed portions of substrate 1410.

[0142] Referring to intermediate structure 1700D, in some embodiments, the mask layer 1431 on one or more nanostructures 1420, 1520, 1620 is removed therefrom. The resist portion of the mask layer 1431 may be removed, for example, by using a liquid resist stripper or an oxygen-based plasma, in a process referred to as ashing. If desired, when included, the underlying hard mask layer may then be removed using a wet or dry etching process that selectively removes the hard mask without substantially affecting the one or more nanostructures 1420, 1520, 1620 or the substrate 1410. An antireflective coating may then be deposited on or on the sides of the nanostructures 1420, 1520, 1620, for example, by spin coating or by chemical vapor deposition and subsequent planarization of the deposited layer.

[0143] In some other embodiments, such as those described above with reference to Figures 10-12, the mask layer 1431, e.g., a photoresist / hard mask or hard mask, may be left in place rather than removed. In these embodiments, the mask layer 1431 may comprise an anti-reflective coating 1430, as described herein with reference to Figures 10-12.

[0144] 14A-14D illustrate cross-sectional views of intermediate structures 1800A-1800D at various stages in the fabrication of optical elements 1400, 1500, and 1600 having metasurfaces 1418, 1518, and 1618, respectively, according to some embodiments. In some embodiments, the method of forming intermediate structures 1800A, 1800C, and 1800D of FIGS. 14A, 14C, and 14D, respectively, is similar to the method of forming intermediate structures 1700A, 1700C, and 1700D of FIGS. 13A, 13C, and 13D, respectively. However, the method of forming intermediate structure 1800B of FIG. 14B differs from the method of forming intermediate structure 1700B of FIG. 13B, and the differences are described below.

[0145] 14B , instead of patterning a photoresist layer by selectively exposing and removing portions of the photoresist using light or an electron beam, in the illustrated embodiment, a nanoimprint template 1432 or nanoimprint mold having a predetermined topological pattern according to the formation of one or more nanostructures 1420, 1520, 1620 is brought into contact with the imprint resist of the mask layer 1431A. In some embodiments, the template 1432 is pressed into the imprint resist, which is formed from a thermoplastic polymer, for example, at a temperature above the glass transition temperature of the imprint resist, thereby transferring the pattern of the template 1432 to the softened imprint resist. After cooling, the template 1432 is separated from the imprint resist, leaving the patterned resist on the high refractive index layer 1411. In some other embodiments, after being pressed into the imprint resist, the imprint resist is hardened by cross-linking under UV light.

[0146] 15, according to some embodiments, after removal of mask layer 1431 from one or more nanostructures 1420, 1520, 1620 as described above with respect to Figures 13D and 14D, an antireflective coating 1430 may be conformally deposited on the nanostructures 1420, 1520, 1620 by a vapor deposition process, such as, for example, a chemical vapor deposition process or an atomic layer deposition process. Thus, in some embodiments, the deposited antireflective coating 1430 may be a conformal layer that covers and follows the contours of the nanostructures 1420, 1520, 1620 without completely filling the volumes separating those nanostructures.

[0147] In the foregoing specification, various specific embodiments have been described. It will be apparent, however, that various modifications and changes can be made therein without departing from the broader spirit and scope of the invention. The specification and drawings are, therefore, to be regarded in an illustrative rather than a restrictive sense.

[0148] Indeed, it should be understood that the systems and methods of the present disclosure each have several innovative aspects, no single one of which is solely responsible for or required for the desirable attributes disclosed herein. The various features and processes described above may be used independently of one another or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of the present disclosure.

[0149] Certain features described herein in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable subcombination. Furthermore, while features may be described above as operative in a combination and may even be initially claimed as such, one or more features from the claimed combination may, in some cases, be deleted from the combination, and the claimed combination may be directed to a subcombination or a variation of the subcombination. No single feature or group of features is required or essential to every embodiment.

[0150] It should be understood that conditional statements used herein, such as "can," "could," "might," "may," "eg," and the like, in particular, are generally intended to convey that certain embodiments include certain features, elements, and / or steps, while other embodiments do not, unless specifically stated otherwise or understood otherwise within the context as used. Thus, such conditional statements are generally not intended to imply that features, elements, and / or steps are in any way required for one or more embodiments, or that one or more embodiments necessarily include logic for determining whether those features, elements, and / or steps are included or should be performed in any particular embodiment, with or without authorial input or prompting. The terms "comprise," "include," "have," and the like are synonymous and used inclusively in a non-limiting manner and do not exclude additional elements, features, acts, operations, etc. Also, the term "or" is used in its inclusive sense (and not its exclusive sense); thus, for example, when used to connect a list of elements, the term "or" means one, some, or all of the elements in the list. Additionally, the articles "a," "an," and "the," as used in this application and the appended claims, should be interpreted to mean "one or more" or "at least one," unless otherwise specified. Similarly, while operations may be depicted in the figures in a particular order, it should be recognized that such operations need not be performed in the particular order or sequential order shown, or that all of the depicted operations need not be performed, to achieve desirable results. Furthermore, the figures may diagrammatically depict one or more exemplary processes in the form of a flowchart. However, other operations not depicted may also be incorporated within the diagrammatically depicted exemplary methods and processes. For example, one or more additional operations may be performed before, after, concurrently with, or during any of the depicted operations.Additionally, operations may be rearranged or reordered in other embodiments. In some situations, multitasking and parallel processing may be advantageous. Furthermore, the separation of various system components in the above-described embodiments should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems may generally be integrated together in a single software product or packaged into multiple software products. Additionally, other implementations are within the scope of the following claims. In some cases, the actions recited in the claims can be performed in a different order and still achieve desirable results.

[0151] Thus, the claims are not intended to be limited to the implementations shown herein but are to be accorded the widest scope consistent with the present disclosure, the principles, and novel features disclosed herein.

Claims

1. 1. A display system, comprising:

1. A waveguide assembly for receiving and outputting image light having image content, the waveguide assembly comprising: an optically transmissive substrate; 1. An internal coupling optical element configured to direct light into the substrate at an angle such that the light propagates through the substrate by total internal reflection, the internal coupling optical element comprising a metasurface overlying the substrate, the metasurface comprising a plurality of nanostructures forming repeating unit cells, each unit cell having, when viewed from above, a plurality of first nanostructures having the same first length and first width elongated in a first direction, one of the first widths being different from another of the first widths; a plurality of second nanostructures having the same second length and second width elongated in a second direction, one of the second widths being different from another of the second widths; an internal coupling optical element, a waveguide assembly comprising: an anti-reflective coating comprising a layer of optically transparent material conformally disposed over the nanostructures of the metasurface; Equipped with a first nanostructure having a first width and a second nanostructure having a second width, the first width being different from the first width of the first nanostructures and the second width being different from the second width of the second nanostructures, the second nanostructure having a first width being different from the first width of the first nanostructures and the second nanostructure having a second width being different from the first width of the second nanostructures, the second nanostructure having a first width being different from the second width of the second nanostructures, the first width being different from the second width of the second nanostructures, the second nanostructure having a first width being different from the first width of the first nanostructures and the second nanostructure having a second width being different from the first width of the second nanostructures, the second nanostructure having a first ...

2. The display system of claim 1 , wherein the anti-reflective coating is an interference coating.

3. The display system of claim 1 , wherein the optically transparent material has a refractive index less than that of the nanostructures.

4. The display system of claim 1 , wherein the optically transparent material comprises a polymer.

5. The display system of claim 4 , wherein the polymer comprises a photoresist.

6. 10. The display system of claim 1, wherein said optically transparent material has a refractive index of about 1.2 to about 2.

7. the waveguide assembly comprising a plurality of substrates forming a substrate stack, each substrate having an associated internal coupling optical element; 10. The display system of claim 1, wherein, when viewed from above, the intercoupling optical elements of different ones of the substrates are laterally offset from one another.

8. The display system of any one of claims 1 to 7, wherein the antireflective coating reduces an amount of incident light reflected by the metasurface by more than about 50% compared to the amount of incident light reflected by a substantially similar metasurface not including the antireflective coating, the incident light having an angle of incidence between about -20° and 20°.

9. 1. A method for forming an anti-reflective coating on a metasurface, the method comprising: providing an optically transmissive substrate comprising a metasurface, the metasurface comprising a plurality of nanostructures forming repeating unit cells, each unit cell, when viewed from above, comprising: a plurality of first nanostructures having the same first length and first width, the first lengths being elongated in a first direction and the first widths being different from one another; a plurality of second nanostructures having the same second length and second width, the second lengths being elongated in a second direction and the second widths being different from one another; wherein the second direction intersects the first direction; and depositing a layer of optically transparent material over the plurality of nanostructures; Including, the layer of optically transparent material forms the anti-reflective coating; the optically transmissive substrate forms a waveguide assembly, the layer of optically transparent material follows the contours of the nanostructures without completely filling the volumes separating each of the nanostructures such that a top surface of each waveguide is non-planar, and the unfilled volumes separating the first nanostructure from the second nanostructure are at a different location than the unfilled volumes separating different first ones of the first nanostructures or different second ones of the second nanostructures, such that at least one of the nanostructures is adjacent to a first unfilled volume having a first width and adjacent to a second unfilled volume having a second width, the first width being different from the second width.

10. The method of claim 9 , wherein the optically transparent material comprises a polymer.

11. The method of claim 10 , wherein the polymer comprises a photoresist.

12. The method of any one of claims 9 to 11, wherein depositing the layer of optically transparent material comprises spin-coating the optically transparent material over the nanostructures.

13. The method of any one of claims 9 to 11, wherein depositing the layer of optically transparent material comprises performing a chemical vapor deposition (CVD) process.

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